The New Radio (NR) definition in 3GPP (3rd Generation Partnership Project) for mobile systems will encompass a variety of deployment scenarios envisioned for 5G (fifth generation) mobile communication systems. MIMO (multiple input, multiple output) communication systems can be used for 5G TDD (time division duplex) air interfaces. Flexible (scalable) frame structures are being considered for block symbol transmissions within the new 5G cellular communication standard including various frame structure parameters such as FFT (fast Fourier transform) size, sample rate, and subframe length.
FIG. 1A (Prior Art) is a diagram of an example embodiment including a base station 102 with M antennas 104 that provides a wireless MIMO communication system 100. The MIMO base station 102 communicates through its M antennas 104 with K different user equipment (UE) devices 106, such as mobile handsets, having one or more antennas 108. Spectral efficiency is improved by using massive MIMO communication systems having base stations with relatively large numbers of antennas. Example embodiments for massive MIMO communication systems are described within U.S. Published Patent Application 2015/0326286, entitled “MASSIVE MIMO ARCHITECTURE,” U.S. Published Patent Application 2015/0326383, entitled “SYNCHRONIZATION OF LARGE ANTENNA COUNT SYSTEMS,” and U.S. Published Patent Application 2015/0326291, entitled “SIGNALING AND FRAME STRUCTURE FOR MASSIVE MIMO CELLULAR TELECOMMUNICATION SYSTEMS,” each of which is hereby incorporated by reference in its entirety.
FIG. 1B (Prior Art) provides a diagram of an example time-domain subframe structure for the LTE (long term evolution) wireless cellular communication standard including a common subframe 102 and OFDM (orthogonal frequency division multiplex) symbols 108. For example, with respect to the 20 MHz (mega-Hertz) bandwidth LTE mode with a normal cyclic prefix 114 and a sampling rate of 30.72 MSps (mega samples per second), one example subframe structure can be parameterized as follows:                OFDM symbol 108 length: 2048 samples;        common cyclic prefix (CP) 114 length: 144 samples;        special cyclic prefix (CP) 112 length: 160 samples        multiple OFDM symbols 108 (with CP); and        subframe 102 length: 1 ms (millisecond) including 14 OFDM symbols (with CP).        
One objective for the 5G air interfaces is to operate from below 1 GHz to 100 GHz carrier frequencies over a large variety of deployment scenarios in a single technical framework, for example, using OFDM (orthogonal frequency division multiplexing) modulation. For this objective, phase noise (PN) becomes a major impairment at carrier frequencies above 6 GHz. Phase noise introduces two kinds of impairment on OFDM-based systems: (1) common phase error (CPE) and (2) inter-carrier interference (ICI). CPE is a common phase rotation across all of the subcarriers for an OFDM transmission, and CPE manifests as a common rotation of the demodulated constellation. The phase noise at each subcarrier frequency also introduces ICI to the neighboring subcarriers, and this spectral leakage degrades the orthogonality of the OFDM waveform. This degradation is manifested as a “fuzziness” in each demodulated constellation point, and the level of ICI can be measured by the degradation of the EVM (Error Vector Magnitude) of the communication link. Phase noise typically increases with the carrier frequency, for example, one general assumption is that PSD (power spectrum density) associated with phase noise increases by about 20 dB per decade of frequency.
CPE can be estimated in a straightforward manner with a least squares estimator according to the equation shown below.
                    J        ^            0        ⁡          (      m      )        =                              ∑                      k            ∈                          S              p                                                                      ⁢                                            R              k                        ⁡                          (              m              )                                ⁢                                    X              k              *                        ⁡                          (              m              )                                ⁢                                    H              k              *                        ⁡                          (              m              )                                                            ∑                      k            ∈                          S              p                                      ⁢                                                                                          X                  k                                ⁡                                  (                  m                  )                                            ⁢                                                H                  k                                ⁡                                  (                  m                  )                                                                          2                      .  For this equation, Rk is the received subcarrier values; Xk, where k∈Sp, is the transmitted pilot symbol that is known at the receiver; Hk is the channel estimate; and Sp is the subset of the subcarriers occupied by the pilot. The CPE for each OFDM symbol within an OFDM transmission is the DC component of the DFT (discrete Fourier transform) of the baseband PN (Phase Noise) samples over that symbol duration.
As CPE is constant for all subcarriers within an OFDM symbol and can be estimated, CPE compensation can be performed with the introduction of Phase Noise Reference Signals (PNRS), also called Phase Tracking Reference Signals (PTRS), or other pilots within the OFDM transmissions. The addition of the PNRS/PTRS, therefore, allows for CPE compensation but only at the expense of additional pilot signal overhead within the OFDM symbols. This CPE estimation based on a static pilot pattern, therefore, has the drawback of high overhead due to required pilot signaling for the purely pilot aided PN compensation. Moreover, different devices and deployment scenarios have different levels of requirement for the PN (phase noise) mitigation. For example, UEs (user equipment) and base stations have significantly different phase noise PSD requirements, and UEs can be categorized into different groups with respect to PN performance based on their frequency band of operation and wireless system application, such as eMBB (enhanced Mobile BroadBand), URLLC (ultra-reliable low latency communications), mMTC (massive machine type communications), and/or other use cases.
It is noted that the terminology Phase Noise Reference Signal (PNRS) is used herein interchangeably with Phase Tracking Reference Signal (PTRS) to refer to the same signal. In addition to OFDM waveforms, PNRS/PTRS can also be inserted in SC (Single Carrier) waveforms in a straightforward manner to estimate and compensate the complete PN (Phase Noise) over that SC waveform. Examples of such single carrier waveforms include Single Carrier Frequency Division Multiple Access (SC-FDMA), DFT spread OFDM (DFT-s-OFDM), Null Cyclic Prefix Single Carrier (NCP-SC), etc.
PTRS (phase tracking-reference signal) ports and related signals can be used by base stations(s) to allow the UEs to derive a scalar estimation of the common phase error (CPE) due to the phase noise process which is assumed to be constant over all of the subcarriers of a given symbol of the allocated UE bandwidth. This estimate becomes more accurate with increasing the number of REs (resource elements) allocated to PTRS within the scheduled bandwidth of the given UE. In addition, when multiple antenna ports are used to transmit from the base station(s) to the UE, there can be one-to-one mapping or many-to-one mapping from the DMRS (demodulation reference signal) ports to the PTRS ports. The DMRS ports are used by the base station(s) to provide signals that facilitate demodulation operations within the UEs. While the use of PTRS ports and related communications can help improve CPE compensation, they can also lead to inefficiencies with respect to the use of available bandwidth and difficulties arise in the selection and allocation of the PTRS ports by the base station(s).